[lynx42]

I believe the correct term for the Star, be it White, Yellow, with a circle or without is the "Allied Recognition Sign".

The first use of the circle around the star was for operation 'Husky', the invasion of Sicily in July 1943. The recommended colour of that circle was YELLOW. If yellow was not available then white, red or blue in that order.

One Dodge Weapons Carrier here in OZ, had the yellow circle and the name 'Umpire' on the hood, until the owner restored it and just put the white circle. Thus destroying it's authentic provenance.

The American Armoured Corp, did not like removing their pre-war Yellow Star if favour of the ordered White Star. This order came through in December 1942. Infact General Patton kept the Yellow Star on his Scoutcar, Halftrack and Dodge right through the war.

I have a listing of some of the order numbers for the changes to the Allied Signs through WW2, but as I am shifting house, they are boxed up and put somewhere to be re-discovered at a later time.

Hope this helps.
Regards Rick